Lecture7 Heavy Metals - Bridgewater State University

1 1 Lecture 7 Lecture 7 Lecture 7 Lecture 7 TOXIC Heavy METALSTOXIC Heavy METALSTOXIC Heavy METALSTOXIC Heavy Metals Metallic elements that are denser than other common Metals Mercury, lead, cadmium and arsenic (a semimetal) present the greatest environmental hazard - WHY? Extensively used Toxic Widely distributed Ultimate sink for Heavy Metals are soils and sediments3 Heavy Metals - DensitiesLight metals43 Toxicity of the Heavy Metals : Of the four, Hg is highly toxic in the elementalform All four are dangerous in the followingform: Cations( from soluble compounds) Organometallic( bonded to organic molecules) Exposure through inhalation of Hg vapor from liquid Hg Toxic Heavy Metals : Hg, Pb, Cd and As5Q. Why are they toxic? Due to strong affinity of metal cations (Mn+) for sulfur Sulfhydryl groups, - SH, in many enzymes, react with ingested Mn+ Can deactivate the enzyme => stops or alters metabolic processesMechanism of Heavy metal toxicityFound in proteins (e.)

2 G. enzymes)Toxic Heavy Metals Heavy Metals : Write the balanced chemical reactions that correspond to the reaction of an Hg2+ion (a) with H2S and (b) with R-SH (where R is an organic group) to produce hydrogen ions and an organometallic this what you got?Hg2++ 2 H2S HS Hg SH+ 2H+Hg2++ 2 RSH RS Hg SR + 2H+7 Utilizes a chelating agentthat binds strongly to the metal cationEx. EDTA Source: Harris, Quantitative Chemical Analysis. (6thed., p. 259)Chelation Therapy: Treatment of Heavy metal PoisoningBinds th/ > 1 site6 binding sites (orange) = hexadentateMn2+Gk. chela = claw85 Medical treatment Administers a compound that binds to the metalmore stronglythan does the enzyme. Ex. BALT reatment of Heavy metal Poisoning (Cont.)9 Mode of entry: Elemental Hg through inhalation Ingestion Systemic: Once in the body, it is carried by the bloodstream to the brainToxic Heavy Metals (1) MercuryToxic forms: Elemental (Hg liquid/vapor), and Compounds of mercury Inorganic salts ex.

3 Mercuric nitrate, Hg(NO3)2 Organometallic ex. methylmercury Transdermal: Hg ( organomercury) can also enter the body by absorption through the skin106 Toxic Heavy Metals : Mercury of health effects from mercury exposure depends on: the chemical form of mercury; the dose; the age of the person exposed (the fetus is the most susceptible); the duration of exposure; the route of exposure (inhalation, ingestion, dermal contact), and the health of the person exposed. Effects of exposure:11 Effects of exposure:Toxic Heavy Metals : Mercury Cont.(1) Elemental mercury effects Tremors; Emotional changes ( , mood swings, irritability, nervousness, etc.); Insomnia; Neuromuscular changes (such as weakness, muscle atrophy, twitching); Headaches; Disturbances in sensations; changes in nerve responses; performance deficits on tests of cognitive function.

4 At higher exposures there may be: Kidney damage, Respiratory failure, and Death 127 Toxic Heavy Metals : Mercury Cont. Exposure in the womb (which can result from a mother's consumption of fish and shellfish that contain methylmercury), can adversely affect a baby's growing brainand nervous system. Impacts on cognitive thinking, memory, attention, language, and fine motor and visual spatial skillshave been seen in children exposed to methylmercury in the womb.(2) Organomercury effects Ex. Methylmercury13 Toxic Heavy Metals : Mercury exposures to inorganic mercury may result in damage to: Gastrointestinal tract, Nervous system, and Kidneys (3) Inorganic mercury effectsReference: US EPA, "Mercury: Health Effects" available at 148 Mercury is the only common metal liquidat ordinary temperatures.

5 Mercury is sometimes called quicksilver. It rarely occurs free in nature and is found mainly in cinnabar ore(HgS) in Spain and Italy. It is a Heavy , silvery-white liquid metal . It alloys easily with many Metals , such as gold, silver, and tin. These alloys are called amalgams. Its ease in amalgamating with gold is made use of in the recovery of gold from its available at : Mercury The first emperor of unified China, Qin Shi Huang, reportedly died of ingesting mercury pills that were intended to give him eternal life. [43] The phrase mad as a hatter is likely a reference to mercury poisoning, as mercury-based compounds were once used in the manufacture of felt hats in the 18th and 19th century. (The Mad Hatter character of Alice in Wonderland was almost certainly inspired by an eccentric furniture dealer, not by a victim of mad hatter disease.)

6 [44] In 1810, two British ships salvaged a large load of elemental mercury from a wrecked Spanish vessel near Cadiz, Spain. The bladders containing the mercury soon ruptured. The element spread about the ships in liquid and vapor forms. The sailors presented with neurologic compromises: tremor, paralysis, andexcessive salivation as well as tooth loss, skin problems, and pulmonary complaints. For years Abraham Lincoln took a common medicine of his time called "blue mass" which contained significant amounts of mercury. 169 History: Mercury Cont. The term Hunter-Russell syndrome derives from a study of mercury poisoning among workers in a seed packing factory in Norwich, England in the late 1930s who breathed methylmercuryused as a seed disinfectantand preservative.[48] Outbreaks of methylmercury poisoning occurred in Minamata, Japan during the 1950s due to industrial discharges of mercury into the Minamata bay.

7 More than 600 people died due to what became known as Minamata disease. In 22 documented cases, pregnant women who consumed contaminated fish showed mild or no symptoms but gave birth to infants with severe developmental disabilities.[2] Widespread mercury poisoning occurred in rural Iraq in 1971-1972, when grain treated with a methylmercury-based fungicideintended for planting only was used by the rural population to make bread, causing at least 459 deaths (see Basra poison grain disaster). [49] 17 History: Mercury Cont. On August 14, 1996, Karen Wetterhahn, a Dartmouth College chemistry professor, spilled a small amount of dimethylmercury on her latex glove. She began experiencing the symptoms of mercury poisoning five months later and, despite aggressive chelationtherapy, died a few months later from brain malfunction due to mercury intoxication.

8 [24][25] On March 19, 2008, Tony Winnett, 55, inhaled mercury vapors while trying to extract gold from computer parts (by using liquid mercury to separate gold from the rest of the alloy), and died ten days later. [51][52] In December 2008, actor Jeremy Piven was diagnosed with hydrargyria resulting from eating sushi twice a day for twenty years. [53] Reference: Wikipedia, Mercury poisoning: History available at #History1810 Mercury(Cont.)Uses: Hg(l)in thermometers,barometersand sphygmomanometer Hg(g)is used in fluorescent bulbsand advertising signs The basis of dental amalgamsand preparations(~ 50% Hg by mass plus other Metals such as Ag, Sn and Cu)US FDA, About Dental Amalgam Fillings , available at amalgam: Image available at Sphygmomanometer (Cont.)When lamp is on, current flows through the electrical circuit to the electrodes.

9 There is a considerable voltage across the electrodes, so electrons will migrate through the inert gas from one end of the tube to the other. This energy changes cause some of the mercury in the tube to vaporize. As electrons and charged atoms collide with the gaseous mercury atoms, the Hg atoms undergo electronic excitation. When the electrons return to their ground State , they release energy in the form of light. HowStuffWorks, 1998-2011 HowStuffWorks, Inc. "How Fluorescent Lamps Work" by Tom Harris, available at (Cont.) Incineration of municipal waste that contain Hg Burning of coaland fuel oil(electric utilities; industries)Sources of Hg contamination of the environment:Contains low levels of Hg Hg spills, from broken thermometersNOTE: Mercury is a naturally-occurring element and exists mainly as cinnabar ore (HgS).

10 21 ~scintech/ (Cont.)Q. Are you familiar with the origin of the expression mad as a hatter ? Mercuric nitrate (source of Hg2+) was used in hat-making in the old days Made the fur fibers soaked in this solution rough and twisted Muscle tremors Workers in hat industry constantly exposed to Hg developed nervous disorder: Depression, memory loss, irritabilityEasily mat togetherMad hatter: Images available at and toxicityMethylmercury Soluble in fatty tissues of animals = more toxic than Hg2+BioaccumulatesBiomagnifiesMercury(Co nt.)2413 Mode of entry: Pb2+: Usually through ingestion of contaminated water and food Pb2+can inhibit the synthesis of hemoglobinEffects: Elemental form is not an environmental problem until it dissolves into Pb2+(or the less stable Pb4+) Interferes with the normal development of children s brains Behavioral effects, including lack of attentiveness Possibly low IQ Adverse effect on the nervous systems (CNS and peripheral) and the kidneysToxic Heavy Metals2)Lead25 Lead is a bluish-white lustrous metal .